It is known in the prior art to provide air suspension systems whereby the vehicle body can be raised or lowered relative to the ground to facilitate the loading of passengers. However, such prior systems have been complicated and have not located the air suspension system in relation to the main body, the wheel-supporting sub-frame, and the steerable wheels so as to minimize the quantity of air to be changed in order to raise and lower the front end of the vehicle to thereby increase the responsiveness of the system in loading and unloading the vehicle while at the same time enhancing the vehicle's transverse or roll stability and lowering the normal height of the floor above the ground.
Today there is an increasing demand for new types of buses, particularly for use in metropolitan areas, which are both more fuel efficient, are easier to repair, and which will more readily accommodate handicapped passengers. As part of the effort to meet these needs, attention is focusing on new types of suspension systems, both front and rear. As shown in his U.S. Pat. No. 4,131,209, Applicant has already developed a new and improved retractable ramp to enable handicapped passengers to have more easy ingress and egress through the front door of a bus. To maximize the effectiveness of such a ramp, an improved bus body design has been developed whereby the vehicle floor is lower to the ground and whereby a single boarding step is possible.
In furtherance of the desire to ease the boarding of handicapped persons, Applicant's invention is directed to a new and simplified front wheel suspension system whereby the front end of a bus may be easily lowered to facilitate passenger loading and unloading, and further which ability is particularly critical for passengers confined to wheelchairs or having to use walking stands or crutches.
Applicant's system is particularly adapted for use with a vehicle wherein the driver's position and a front entrance are disposed forwardly of the steerable wheels. In order to provide for the normal springing of the vehicle body as well as to provide a "kneeling" feature, the steerable wheels are mounted on the fixed axle or base of a sub-frame the other end of which extends rearwardly and is pivotally articulated to the underbody rearwardly of the steerable wheels.
Various articulated or V-shaped wheel suspension sub-frames are shown in the prior patented art and are typified by the following U.S. Pat. Nos.: 1,479,187 Lansden; 2,132,963 Nallinger; 3,735,999 Blackledge et al; 3,744,813 Magleave; 3,865,396 Bates; and 3,768,825 Magnusson. Applicant's front wheel suspension system differs from the prior art both in the orientation and area of articulation of his sub-frame with respect to the vehicle underbody as well as the location of the air springs between the sub-frame and a transverse beam of the underbody. Furthermore, Applicant's invention locates the front wheel suspension system rearwardly of the steerable wheels and the front end of the bus whereby the suspension system is protected against damage or displacement in the event of a front end collision.
In the type of vehicle with which Applicant's invention is concerned, the vehicle body is most preferably of a monocoque design wherein an upper body is integrally formed with an underbody to eliminate the traditional frame or chassis. Accordingly, Applicant has developed a new type of A-shaped sub-frame which uniquely coacts with the vehicle underbody to support the sprung mass of the vehicle and permits the selective lowering and raising of the front door area of the vehicle to aid in the loading and unloading of handicapped passengers.
In the present invention the vehicle underbody extends laterally or transversely beyond the A-shaped sub-frame such that the steerable wheels are recessed within the underbody and the upper body. The sub-frame includes a transverse axle upon which the steerable wheels are rotatably supported. The sub-frame also includes a transverse cross beam element disposed longitudinally between the axle and the point of articulation of the sub-frame to the underbody. Further, such cross beam element extends laterally so as to terminate proximate the area where the underbody and upper body are joined. A pair of adjustable air spring members are respectively supported between the outer ends of the cross beam element and the underbody and in generally longitudinal alignment with the steerable wheels.
As typified by the aforementioned Lansden, Blackledge and Nallinger patents, it is common practice to mount sub-frame spring members along or proximate to the axle element rather than intermediate the axle and the point of articulation of a sub-frame and the vehicle body.
The location of the air spring members in relationship to the steerable wheels, the underbody and the A-shaped sub-frame is significant in achieving the desired performance of Applicant's suspension system. In other words, mounting the air spring members on a transverse axis intermediate the steering wheel axle and the point of articulation of the A-shaped sub-frame to the underbody reduces the amount of vertical movement of each spring member necessary to lower and raise the front end of the vehicle and, accordingly, speeds the body raising and lowering action to reduce the time necessary to allow ingress or egress through the front vehicle door. This is a particularly important capability when the suspension system is utilized with a ramp device, such as shown in Applicant's U.S. Pat. No. 4,131,209, for loading and unloading handicapped passengers. Furthermore, the outboard location of the adjustable air spring members in alignment with the steerable wheels transmits spring loads more directly to the vehicle body thereby enhancing its transverse or roll stability.
Various other advantages are achieved with Applicant's invention which is shown in the drawings and hereinafter described in detail.